Will Grigg celebrates scoring Wigan’s second goal with a penalty against West Ham.
Photograph: Chris Brunskill Ltd/Getty Images

A feeble West Ham performance led to David Moyes’s depleted side becoming Wigan Athletic’s latest Premier League victims, in a Cup tie overshadowed by the dismissal of Arthur Masuaku early in the second half for spitting. It will be a pity if the game is remembered only for that, or for a West Ham injury list running into double figures, for this was a lively Wigan performance that was perhaps even better than the one that dumped Bournemouth out in the third round.

Moyes admitted his side had not looked or played like a Premier League team and said Wigan deserved the victory, though his opposite number, Paul Cook, generously suggested the sending off had changed the game. “It was a massive defining moment,” the Wigan manager said. “West Ham had started the second half a lot better but after the red card the game panned out positively for us. It might have been different had it stayed 11 v 11.”

Moyes did not disagree, though neither did he attempt to defend his player’s actions. “Despicable,” he said. “Completely unacceptable. He deserves everything he will get, and he will get something.” Masuaku is most likely looking at a six-match ban – just what Moyes needs during an injury crisis – yet he was not the only player to disappoint his manager. “The young players didn’t seize their chance to impress and the senior players didn’t help them out,” Moyes said.

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Only Manchester City have won more games than Wigan this season, though the home players were looking forward to this tie because it came without the pressure of being expected to deliver. The Latics certainly looked relaxed. Having named his strongest side, Cook came out to watch proceedings with a cup of tea in hand, and before he had finished it the League One leaders were in front. Nathan Byrne was allowed far too much space to run down the right wing and send over a deep cross, and though Will Grigg still needed to summon power and accuracy to beat Joe Hart with a header at the far post, he managed it with aplomb.

The reaction from West Ham was muted, to say the least, and the visitors’ afternoon did not get any better when Pedro Obiang was added to their lengthy treatment list after sustaining medial ligament damage half an hour in. There were practically no threats to the Wigan goal in the first half, save for Sam Byram running offside and Javier Hernández tripping over his own feet, though the latter could possibly have done better with a sharp chance in stoppage time when Antonio Martínez beat Callum Elder to reach the byline and send in a low cross that led to a brief period of pinball in the Wigan goalmouth.

Wigan supporters were sorry to see Pablo Zabaleta replaced at half-time – the former Manchester City player had been losing his temper to the extent that a repeat of his Wembley 2013 dismissal seemed likely – though West Ham still went down to 10 men when Masuaku reacted to a heavy challenge from Nick Powell by spitting at the Wigan player. As Moyes pointed out afterwards, there was no way the referee could have seen the incident, but he produced a straight red when several home players joined Powell’s vehement protest. “I didn’t see anything either, so I asked him did he spit,” Moyes said. “He told me that he did.”

If the impressive West Ham travelling support imagined things could not possibly get any worse – they probably didn’t – there was further ignominy on the hour when Reece Burke gave away a slightly harsh penalty for handling as Grigg attempted to lift the ball past him to set up a shooting opportunity. The Northern Ireland striker beat Hart for a second time from the spot, which led to the home fans telling Moyes he would be sacked in the morning at the same time as the away end was demanding the same fate for the West Ham board.

Grigg could have ended up with a hat-trick had he been slightly quicker in anticipating another juicy cross from the excellent Byrne 10 minutes from the end, one that ended up running harmlessly across the face of goal. No wonder Wigan are worried about losing some of their best players before the end of the transfer window: for a League One side they boast quite a collection.